Cost is a big factor, but so are modern building codes. Some classic architectural features are outright illegal to build in 2026. Others might be allowed, but there's almost no one left who knows how to do it (e.g. plaster walls or ceilings).

Robots are not going to bring any of this back because robots will just create a new set of optimizations and constraints needed to make robotic construction cheaper and easier. If modern cars (which are the result of similar optimization) are anything to go by, this will result in output that's easy to build but hard to maintain or modify - so largely a continuation of existing trends.

Take a look at "3d printed" houses for an imperfect example of this kind of optimization for automation in action. Better robotics will bring about a more balanced version of this trade-off (walls will probably be possible to modify, unlike 3d printed ones) but the incentives remain the same.

Edit:

Trivial example: One of the easiest way to autonomously insulate a house will probably be with spray foam insulation - you can get a robot arm to hold the sprayer and move it in a specific, continuous motion pretty readily even today. But spray foam insulation is hard to modify after the fact. Removing it is time-intensive compared to removing insulation "batting" and applying it again requires specialized tools, PPE, and perhaps licensing.